1. Field of the Invention
This invention relates to flexible connections for conducting load current in electric power switches between a moveable contact support and a fixed conductor.
2. Background Information
Electric power switches require an arrangement for conducting the load current between a moveable contact of the switch and a fixed conductor. The requirements for such an arrangement are many and include such things as: adequate current carrying capability, adequate motion capacity and directional ability, minimum force/energy requirements, temperature withstand ability, ability to retain shape or integrity under transient conditions, and others. While some electric power switches utilize sliding connectors for this purpose, the most common connection is a flexible conductor or shunt.
In electric power switches with lower current ratings, a braided copper conductor is often used as the flexible shunt. At higher current ratings, such as in medium voltage circuit breakers, it is known to utilize a flexible conductor made up of a stack of thin copper laminations. These laminations have been at least 0.003 inches (0.076 mm), and in some cases as much as 0.040 inches (1.016 mm), thick. The laminated conductors to date have been relatively long compared to the stroke, that is the movement required to open and close the switch. They have also required an appreciable force to operate. In some applications, the laminated shunt is installed in a C configuration which requires a long conductor and takes considerable space in two dimensions. In another arrangement, a V fold is provided in the laminated shunt. This latter arrangement is very effective, but again, requires a long shunt and considerable space in two dimensions.
With the trend toward more compact electric power switches with higher current ratings, an improved flexible shunt is needed. The currently available flexible conductors or shunts have been found to be either too large, too expensive, not reliable enough or require too much force to operate, or to have combinations of these limitations.
This invention is directed to an improved flexible shunt for electrically connecting an electric power switch moveable contact support member reciprocating along a linear path to a stationary termination positioned laterally of the linear path. This flexible shunt includes a flexible member comprising a stack of electrically conductive laminations having an intermediate section of predetermined length between a fixed end and the moveable end. A moveable mount secures the moveable end of the flexible member to the moveable contact support member for movement over a stroke extending along the linear path between a closed position at one end of the stroke and an open position at the other end of the stroke. A fixed mount secures the fixed end of the flexible member to the stationary conductor termination with the fixed end spaced from the moveable end along a neutral axis which is substantially perpendicular to the linear path of the moveable contact support by an offset distance which is less than the predetermined length of the intermediate section. The stroke of the moveable contact member is at least about one-third of the predetermined length of the intermediate section and can be at least about one-half the length of the intermediate section. Preferably, the fixed mount and the moveable mount mount the respective ends of the flexible member with the laminations extending substantially perpendicular to the linear path. The laminations can be joined together at the ends, or alternatively, can be plated to reduce the interface resistance between laminations.
The laminations of the flexible member of the invention are very thin. More particularly, the laminations are no greater than about 0.002 inches (about 0.051 mm) thick and preferably no more than about 0.0015 inches (about 0.038 mm) thick. Depending upon the ampacity required, the flexible member can have at least about 100 laminations and in some applications at least about 200 laminations.
The flexible shunt of the invention is particularly suitable for use with vacuum interrupters. Such interrupters can have a stroke, including tolerances and wear, of at least about 0.6 inches (about 15 mm) and even at least about 0.787 inches (about 20 mm). Thus the moveable end of the flexible member must be capable of reciprocating along the linear path at least these distances. Even with the stroke of about 0.787 inches (about 20 mm) the length of the intermediate section of the flexible member need be no more than about 1.5 inches (about 38.1 mm).